The left side of a human heart includes the left atrium (LA) and the left ventricle (LV). An aorta receives oxygenated blood from the left ventricle through an aortic valve, which serves to prevent regurgitation of blood back into the left ventricle. A mitral valve is positioned between the left atrium and the left ventricle and allows one-way flow of the oxygenated blood from the left atrium to the left ventricle.
Mitral valve, which will be described below in more detail, includes an anterior leaflet and a posterior leaflet that are coupled to chordae tendineae. Chordae tendineae serve as “tension members” that prevent the leaflets of the mitral valve from moving past their closing point and prolapsing back into the left atrium. When the left ventricle contracts during systole, chordae tendineae limit the upward motion (toward the left atrium) of the anterior and posterior leaflets past the point at which the anterior and posterior leaflets meet and seal to prevent backflow from the left ventricle to the left atrium (“mitral regurgitation” or “mitral insufficiency”). Chordae tendineae arise from a columnae carnae or, more specifically, a musculi papillares (papillary muscles) of the columnae carnae. In various figures herein, some anatomical features have been deleted solely for clarity.
The anterior leaflet and the posterior leaflet of the mitral valve are generally thin, flexible membranes. When the mitral valve is closed, the anterior leaflet and the posterior leaflet are generally aligned and contact one another along a “line of coaptation” several millimeters back from their free edges, to create a seal that prevents mitral regurgitation. Alternatively, when the mitral valve is opened, blood flows downwardly through an opening created between the anterior leaflet and the posterior leaflet into left ventricle.
Many problems relating to the mitral valve may occur and may cause many types of ailments. Such problems include, but are not limited to, mitral regurgitation. Mitral regurgitation, or leakage, is the backflow of blood from the left ventricle into the left atrium due to an imperfect closure of the mitral valve. That is, leakage often occurs when the anterior and posterior leaflets do not seal against each other, resulting in a gap between the anterior leaflet and the posterior leaflet when the leaflets are supposed to be fully coapted during systole.
In general, a relatively significant systolic gap may exist between the anterior leaflet and the posterior leaflet for a variety of different reasons. For example, a gap may exist due to congenital malformations, because of ischemic disease, or because the heart has been damaged by a previous heart attack. Such a gap may also be created when congestive heart failure, e.g., cardiomyopathy, or some other type of distress which causes a heart to be enlarged. Enlargement of the heart can result in dilation (stretching) of the mitral annulus. This enlargement is usually limited to the posterior valve annulus and is associated with the posterior leaflet, because the anterior annulus is a relatively rigid fibrous structure. When the posterior annulus enlarges, it causes the posterior leaflet to move away from the anterior leaflet, causing a gap during systole because the two leaflets no longer form proper coaptation. This results in leakage of blood through the valve or regurgitation.
Blood leakage through the mitral valve generally causes a heart to operate less efficiently, as the heart pumps blood both out to the body via the aorta, and also back (in the form of mitral regurgitation) into the left atrium. Leakage through the mitral valve, or general mitral insufficiency, is thus often considered to be a precursor to congestive heart failure (CHF) or a cause of progressive worsening of heart failure. There are generally different levels of symptoms associated with heart failure. These levels are classified by the New York Heart Association (NYHA) functional classification system. The levels range from a Class 1 level which is associated with an asymptomatic patient who has substantially no physical limitations to a Class 4 level which is associated with a patient who is unable to carry out any physical activity without discomfort and has symptoms of cardiac insufficiency even at rest. In general, correcting or reducing the degree of mitral valve leakage may be successful in allowing the NYHA classification grade of a patient to be reduced. For instance, a patient with a Class 4 classification may have his classification reduced to Class 3 or Class 2 and, hence, be relatively comfortable at rest or even during mild physical exertion. By eliminating the flow of blood backwards into the left atrium, therapies that reduce mitral insufficiency reduce the workload of the heart and may prevent or slow the degradation of heart function and congestive heart failure symptoms that is common when a significant degree of mitral insufficiency remains uncorrected.
Treatments used to correct for mitral valve leakage or, more generally, CHF, are typically highly invasive, open-heart surgical procedures. In extreme cases, this may include implantation of a ventricular assist device such as an artificial heart in a patient with a failing heart. The implantation of a ventricular assist device is often expensive, and a patient with a ventricular assist device must be placed on extended anti-coagulant therapy. Anti-coagulant therapy reduces the risk of blood clot formation for example, within the ventricular assist device. Reducing the risks of blood clots associated with the ventricular assist device is desirable, but anti-coagulant therapies may increase the risk of uncontrollable bleeding in a patient, e.g., as a result of a fall.
Rather than implanting a ventricular assist device, bi-ventricular pacing devices similar to pacemakers may be implanted in some cases, e.g., cases in which a heart beats inefficiently in a particular asynchronous manner. While the implantation of a bi-ventricular pacing device may be effective, not all heart patients are suitable for receiving a bi-ventricular pacing device. Further, the implantation of a bi-ventricular pacing device is expensive, and is generally not effective in significantly reducing or eliminating the degree of mitral regurgitation.
Open-heart surgical procedures that are intended to correct for mitral valve leakage, specifically, can involve the implantation of a replacement valve. Valves from animals, e.g., pigs, may be used to replace a mitral valve in a human. While a pig valve as a replacement for the mitral valve may be relatively successful, such replacement valves generally wear out, thereby requiring additional open surgery at a later date. Mechanical valves, which are less likely to wear out, may also be used to replace a leaking mitral valve. However, when a mechanical valve is implanted, there is an increased risk of thromboembolism, and a patient is generally required to undergo extended anti-coagulant therapies.
A less invasive surgical procedure involves heart bypass surgery associated with a port access procedure. For a port access procedure, the heart may be accessed by cutting between ribs or sometimes removing parts of one or more ribs, as opposed to dividing the sternum to open the entire chest of a patient.
One open-heart surgical procedure that is particularly successful in correcting a mitral valve leakage and, in addition, mitral regurgitation, is an annuloplasty procedure. During an annuloplasty procedure, a medical device such as an annuloplasty ring may be implanted surgically on the left atrial side of mitral annulus (i.e., generally the attachment location of the base of the mitral valve to the heart). The device reduces a dilated mitral valve annulus to a relatively normal size and, specifically, moves the posterior leaflet closer to the anterior leaflet to aid anterior-posterior leaflet coaptation and thus improve the quality of mitral valve closure during systole. Annuloplasty rings are often shaped substantially like the letter “D” to correspond to the natural shape of the mitral annulus as viewed from above. Typically, the rings are formed from a rod or tube of biocompatible material, e.g., plastic, that has a DACRON mesh covering.
In order for an annuloplasty ring to be implanted, a surgeon surgically attaches the annuloplasty ring to the mitral valve on the atrial side of the mitral valve. Conventional methods for installing a ring require open-heart surgery which involves opening a patient's sternum and placing the patient on a heart bypass machine. The annuloplasty ring is sewn on a top portion of the mitral valve. In sewing the annuloplasty ring onto the mitral valve, a surgeon generally sews the straight side of the “D” to the fibrous tissue located at the junction between the posterior wall of the aorta and the base of the anterior mitral valve leaflet. As the curved part of the ring is sewn to the posterior aspect of the annulus, the surgeon alternately acquires a relatively larger amount of tissue from the mitral annulus, e.g., a one-eighth inch bite of tissue, using a needle and thread, compared to a relatively smaller bite taken of the fabric covering of the annuloplasty ring. Once the thread has loosely coupled the annuloplasty ring to the mitral valve annulus tissue, the annuloplasty ring is slid into contact with the mitral annulus. The tissue of the posterior mitral annulus that was previously stretched out, e.g., due to an enlarged heart, is effectively reduced in circumference and pulled forwards towards the anterior mitral leaflet by the tension applied by annuloplasty ring with the suture or thread. As a result, a gap between the anterior leaflet and the posterior leaflet during ventricular contraction or systole may be reduced and even substantially closed off in many cases thereby significantly reducing or even eliminating mitral insufficiency. After the mitral valve is shaped by the ring, the anterior and posterior leaflets will reform typically by pulling the posterior leaflet forward to properly meet the anterior leaflet and create a new contact line that will enable the mitral valve to appear and to function properly.
Although a patient that receives an annuloplasty ring may be subjected to anti-coagulant therapies, therapies are not extensive, as a patient is only subjected to therapies for a matter of weeks, e.g., until tissue grows over the annuloplasty ring.
Another type of procedure that is generally effective in reducing mitral valve leakage associated with prolapse of the valve leaflets involves placing a single edge-to-edge suture in the mitral valve that opposes the mid-portions of anterior and posterior leaflets. For example, in an Alfieri stitch or a bow-tie repair procedure, an edge-to-edge stitch is made at approximately the center of the gap between an anterior leaflet and a posterior leaflet of a mitral valve. Once the stitch is in place between the anterior and posterior leaflets, it is pulled in to form a suture which holds the anterior leaflet against the posterior leaflet.
Another surgical procedure that reduces mitral valve leakage involves placing sutures along a mitral valve annulus around the posterior leaflet. These sutures may be formed as a double track, e.g., in two “rows” from a single strand of suture material. The sutures are tied off at approximately a central point of posterior leaflet. Pledgets are often positioned under selected sutures to prevent the sutures from tearing through annulus. When the sutures are tightened and tied off, the circumference of the annulus may effectively be reduced to a desired size such that the size of a systolic gap between posterior leaflet and an anterior leaflet may be reduced.
While invasive surgical procedures have proven to be effective in the treatment of mitral valve leakage, invasive surgical procedures often have significant drawbacks. Any time a patient undergoes open-heart surgery, there is a risk of infection. Opening the sternum and using a cardiopulmonary bypass machine has also been shown to result in a significant incidence of both short and long term neurological deficits. Further, given the complexity of open-heart surgery, and the significant associated recovery time, people that are not greatly inconvenienced by CHF symptoms, e.g., people at a Class 1 classification, may choose not to have corrective surgery. In addition, people that need open heart surgery the most, e.g., people at a Class 4 classification, may either be too frail or too weak to undergo the surgery. Hence, many people that may benefit from a surgically repaired mitral valve may not undergo surgery.
In another method, a cinching device is placed within the coronary sinus (CS) using a catheter system, with distal, mid, and proximal anchors within the lumen of the CS to allow plication of the annulus via the CS. In practice, these anchors are cinched together and the distance between them is shortened by pulling a flexible tensile member such as a cable or suture with the intent being to shorten the valve annulus and pull the posterior leaflet closer to the anterior leaflet in a manner similar to an annuloplasty procedure. Unfortunately, since the tissue that forms the CS is relatively delicate, the anchors are prone to tear the tissue during the cinching procedure. In addition, the effect on the mitral annulus may be reduced when the CS of a particular patient is not directly aligned with the mitral annulus. Other minimally invasive techniques have been proposed but have various drawbacks related to such factors as effectiveness and/or accuracy of catheter-based implementation.
Catheter-based surgical procedures have been used to repair a defective mitral valve. Specifically, anchors are secured at a plurality of locations distributed around the annulus near the posterior leaflet of a mitral valve. Each anchor has a suture coupled thereto. The sutures are collectively gathered and pulled tight. As the sutures are pulled, the tissue between each pair of adjacent anchors is plicated, thereby shortening the length of the annulus and drawing the posterior leaflet toward the anterior leaflet. Similar techniques can also be used to repair a defective tricuspid valve.
During a surgical procedure, anchors are usually introduced and secured sequentially. A typical repair by using the catheter based surgical procedure involves a sequence that includes introducing a catheter to a proximity of the annulus, making an incision at the annulus, introducing a guide wire through the incision site, withdrawing the catheter, introducing an anchor by tracking a second catheter through the guide wire, securing the anchor in the annulus, and withdrawing the second catheter. This sequence is repeated to secure a second anchor.
Catheters capable of delivering multiple guide wires or anchors have been disclosed. Without claiming to have exhaustively examined prior art references and without attempting to characterizing any prior art reference, U.S. Patent Application Publication No. 2008-0228265 discloses a triple lumen catheter. However, distances between two of the three lumens are usually fixed. In addition, during a deployment, the two outer catheters are generally advanced lengthwise as well as laterally. In certain instances, one or both of the two outer catheters are caught by chordae tendineae during the deployment.
There is generally a need for an improved catheter to simplify the catheter-based mitral valve correction.